There are many genes involved in determining hair color or eye color. They call this type of trait polygenic. So if you think about all the variation that may come with having multiple genes that may or may not cross over and mutate, there are a lot of combinations. But you're right, why is it that it is typical to see blonde hair/blue-eyed people? This happens to be because the genes that code for hair color are on the same chromosome and close to the genes that code for hair color. Since they are close to one another, they tend to travel as a pair during the DNA swap between mom and dad chromosomes. The genes don't always travel together, though, and mutations influence how these genes are read, so that's why you can see brunettes with blue eyes, too, for example.
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